Machine tool spindles use tool holders, such as HSK or CAT type tool holders, to allow for the facile and automatic changing of tools. The tool holders accommodate different size tools through the use of inserts or collets, and they rigidly clamp a tool at its inner end (shank) so that the dominant compliance is the cantilevered tool itself. Long tools, particularly, are prone to vibration and chatter, and their holders provide little damping. Some inserts use hydraulic fluid to create pressure on a membrane which squeezes the tool (a typical unit is sold under the name HydroLock), but then fluid film gaps are large, and the pressure is isostatic, and the clamping/damping is applied at one point only, so bending moments are poorly resisted/damped.